Fluorescence occurs when a substance receiving a light of a certain color (excitation) emits a light of a different color (emission). The wavelength of the emission is typically longer than that of the excitation. A fluorometer is a device that measures fluorescence by supplying an excitation source, detecting the resulting emission, and converting the emission into an electrical signal proportional to fluorescence. This electrical signal can be used to drive a display to show the fluorescent signal and/or used as a control signal for controlling processes. There are various implementations of fluorometers. A spectrofluorometer allows the user to select the excitation and/or emission wavelengths. A scanning spectrofluorometer can scan the excitation and/or emission over a range of wavelengths.
Fixed filter fluorometers are used when low cost and/or reliability are desirable. Fixed filter fluorometers have a light source with an optional filter to select an optimal excitation wavelength. The detector also has a filter to select the optimal emission wavelength, which is different from the excitation wavelength. Typically, the excitation source and the emission detector are positioned at a 90° angle from each other, though this may change depending on the application.
Fluorometers are used in a wide variety of applications, including but not limited to environmental studies, leak detection, dye tracer studies, and industrial control. In industrial control applications, an inert fluorescent tracer is bonded with a control chemical of interest (for example, a biocide to prevent biological growth within a cooling system). The quantity of the fluorescent tracer is directly proportional to the control chemical. As the control chemical is consumed the amount of fluorescent tracer will drop. Using a fluorometer to detect the amount of fluorescent tracer allows the user to indirectly measure the control chemical. Using this fluorescent measurement the user can accurately control the amount of control chemical in the system. This can be as simple as turning on a pump when the fluorescent signal drops to a certain level (thus adding the control chemical to the system) and turning off the pump when the fluorescent signal reaches a desired level. More complex algorithms can be used as well.
A limitation of current fixed filter fluorometers for industrial control is that they must be supplied a water stream from the system of interest. Additional plumbing must be installed, usually with safety features, to supply water to the fluorometer and to either return the water to the system or dispose of it. This additional plumbing adds cost, labor, and complexity to the system. These fluorometers usually have a flow cell, which is a clear tube through which the sample water flows so that the fluorescence can be detected. This flow cell can become fouled (become less optically clear) which reduces the fluorescent signal. If the flow cell remains fouled then an error is introduced into the control of the system. Since this is undesirable, a periodic maintenance is usually required to clean the flow cell, again adding undesirable labor and cost. An example of such a fluorometer is described in U.S. Pat. No. 6,369,894.
Therefore, there exists a need for a fluorometer that can be introduced directly into a stream of non-solid material. This greatly reduces the installation requirements for the fluorometer and eliminates the flow cell, thus reducing maintenance requirements. More generally, there is a need for a spectrometer that can easily be introduced into a stream of a non-solid material.